It is well-established that, for the production of sound copper castings, complete elimination of hydrogen and oxygen is absolutely necessary. The method usually adopted in copper founding to avoid the steam reaction is the oxidation-reduction melting practice, which consists in keeping the hydrogen content of the melt low by increasing the oxygen content, which is subsequently removed by suitable deoxidation. For routine foundry control of gas induced porosity, a knowledge of the oxygen level in the melt prior to final deoxidation is required, since any excess of deoxidant is not only expensive but harmful. The method used in copper refineries, such as the solid electrolytic cell oxygen probe, are generally not suitable for small foundries due to the very high cost of consumables.
A simple, quick and inexpensive test for oxygen assessment in copper foundries relies on a carbon or graphite rod immersed in the oxidized copper melt. The rod will vibrate owing to the C+[O].fwdarw.CO reaction occurring at its surface, the intensity of vibration being a function of the oxygen content. The test is reproducible and can readily determine the point at which the reaction becomes negligible, that is, when the oxygen is reduced to a low level.
J. L. Dion, A. Couture, and J. O. Edwards have used the graphite rod immersed test as a qualitative indication of the oxygen content in the liquid copper [1]. The authors reported only qualitative values of the vibration felt as moderate, slight and almost nil.